1. Field of the Invention
The present invention relates to a turbomolecular pump including a housing having a suction opening and a gas outlet opening, and a plurality of alternatingly arranged one behind another, stator and stator discs provided, respectively, with support rings for supporting each blade.
2. Description of the Prior Art
Vacuum pumps, which are formed as turbomolecular pumps, as a rule, have a plurality of stages formed of alternatingly arranged one behind the other, stator and rotor discs. In order to obtain optimal pump characteristics, such as a maximal compression, the rotor discs should rotate with a very, high speed. The drive energy, which is required to provide for the high speed rotation of the rotor discs, is partially converted into the kinetic energy, a large portion of which is released in form of heat. Other undesirable heat quantities are produced in bearings (mechanical losses resulting from friction in the ball bearings or electrical losses in magnetic bearings) or as a result of the compression of gases. The generated heat can cause overheating of critical components of a turbomolecular pump. This should be prevented. Thus, an effective heat removal is necessary in the turbomolecular pumps.
The heat transfer in vacuum from rotor components to stator components is effected substantially by radiation.
Because rotor and stator discs face each other along large surfaces, a large portion of heat can be transmitted from rotor discs to stator discs by radiation. The stator discs are connected with the housing of a turbomolecular pump by spacer rings, as disclosed, e.g., in German Publication DE-0S 3722164. Because in the turbomolecular pump disclosed in DE-0S 3722164 for transmitting the heat, only minimal contact surfaces are available, the transmission of heat from the stator discs to the housing and, thereby, outwardly is not adequate.
The other factors, which require an adequate heat removal are as follows:
Turbomolecular pumps are primarily used in processes, such as, e.g., chemical process or a manufacturing process for producing semiconductors, which require use of large amounts of process gases. As a rule, these process gases easily condensate, in particular, at low temperatures. This results in a noticeable precipitation of liquid or solids, which cause corrosion and caustic process that can lead to destruction of individual components of a turbomolecular pump or to a destruction of the entire pump.
By heating of corresponding regions liquid and solid precipitation can be eliminated to a large extent, as discussed in German publication DE-0S 197 02 456. The heating is effected with corresponding elements provided on or in the pump housing. However, because, as described above, only minimal contact surfaces between the housing, spacer rings, and stator discs are provided in conventional turbomolecular pumps, the heat transfer between the housing and the stator discs is unsatisfactory.
These two factors, namely, transfer of heat from stator discs to the housing and in the opposite direction, are critical for a reliable operation of a turbomolecular pump.
Accordingly, an object of the present invention is to provide a turbomolecular pump with a noticeably improved heat transfer from the housing to the stator discs and in the opposite direction.
This and other objects of the present invention, which will become apparent hereinafter, are achieved by providing a turbomolecular pump in which a support ring of a stator disc located adjacent to a high pressure region of the turbomolecular pump, is connected with an adjacent housing part over a large surface.
The large-surface contact between the support ring of the stator disc, which is located adjacent to the high-pressure region of the pump, and the adjacent housing parts provides for noticeably better heat transfer between the stator disc and the housing than in conventional turbomolecular pumps.
The objects of the invention are also achieved when the support ring of the stator disc, which is located adjacent to the high pressure region of the pump, is formed integrally, as one-piece, with the adjacent housing part.
A large contact surface between the support ring of the last stator disc with the adjacent housing part or the formation of the support ring of the last stator disc integrally with the adjacent housing part, together with large opposite surfaces of the stator and rotor discs, noticeably increases heat transfer from the rotor discs to the housing and in the opposite direction. The present invention permits to deliver larger quantities of gases at the same rotor temperature.
The formation of a cooling water channel in the connection region of the support ring of the last stator disc with the adjacent housing part or, alternatively, in the housing part further increases heat transfer between the stator disc and the housing.
For heating the stator, heating means can be provided in the support ring or the adjacent housing part in a, space-saving manner. Advantageously, the adjacent housing part is thermally insulated from the rest of the housing. In this way, heating of a critical region of the pump without significant heat losses becomes possible.
The support ring of the last stator disc can be formed either as an inner ring or as an outer ring. This permits to adapt the arrangement according to the present invention to different constructions of turbomolecular pump.
The novel features of the present invention, which are considered as characteristic for the invention, are set forth in the appended claims. The invention itself, however, both as to its construction and its mode of operation, together with additional advantages and objects thereof, will be best understood from the following detailed description of preferred embodiments, when read with reference to the accompanying drawings.